The next day after smoking marijuana the previous night, one tends to feel very chill and lazy about everything. A dumbover is the next step up, but sometimes you don't get a dumbover, just a chillover. If you have a dumbover, you usually have a chillover. If you have a chillover, you don't always have a dumbover.

-"I only smoked a bowl or two last night before bed, so I have a chillover today haha."

-"I didn't go to class today because I had a chillover, so I just played FarmVille instead."